The first 3-D ferrimagnetic nickel fumarate with an open framework: [Ni-3(OH)(2)(O2C-C2H2-CO2)(H2O)(4)]center dot 2H(2)O

A three-dimensional nickel fumarate has been isolated by hydrothermal reaction and its structure solved from powder X-ray diffraction; its organisation reveals an unusual topology not previously seen in nickel chemistry and provided a scarce ferrimagnetic behaviour below 20 K.